This invention relates to a cylinder valve, by which is meant a valve intended to control the flow of gas from a cylinder or other container in which the gas is stored under pressure, and a gas cylinder fitted with the cylinder valve.
Gas cylinders and other containers of compressed gas have been in common use for a long time for the storage of the compressed gas. A gas cylinder has a mouth which is fitted with a cylinder valve. The cylinder valve may be manually opened to release gas from the cylinder and closed again to stop the release of the gas. When the cylinder is empty it is refilled through the cylinder valve. The cylinder valve therefore needs to be of a configuration that permits such refilling to be carried out.
A traditional cylinder valve has a body including a valve seat; a valve member carried on a spindle, and a handwheel in which the spindle terminates. By turning the handwheel in the appropriate direction the valve may be opened and closed. When empty the cylinder may be filled with the valve in the open position.
A disadvantage of this traditional cylinder valve is that when the cylinder is empty or nearly empty backflow of impurities into the cylinder is possible. Such backflow of impurities is particularly undesirable when it is essential to maintain the purity of the gas, for example, when delivering a medical gas.
In order to overcome this disadvantage, some more modern forms of cylinder valve incorporate a second valve in addition to the spindle-operated valve, the second valve having a spring-loaded shuttle member, the spring acting against the pressure of the gas. When the pressure in the cylinder falls so low that it is no longer able to overcome the bias of the spring, the shuttle valve closes and the cylinder is no longer able to delivery gas. A positive pressure is therefore always maintained in the cylinder to prevent the backflow of impurities. The second valve is therefore sometimes referred to as a “residual pressure” or “minimum pressure” valve. Different configurations of the two valves in a single body are possible, but they all add to the complexity of the arrangement. An example of one possible configuration is given in GB patent specification 1 319 764.
It is an aim of the present invention to provide a simple cylinder valve which nonetheless retains the features of manual shut-off and maintenance of a residual pressure.